DEVICE AND METHOD FOR MACHINING A SURFACE OF A WORKPIECE

Abstract

A device for machining a surface of a workpiece includes a workpiece holder configured to rotate the workpiece about a workpiece rotational axis, a tool having a tool rotational axis and at least one blade having a blade radius of curvature and a tool holder configured to position the tool such that an active point of the blade comes into engagement with the workpiece and configured to pivot the tool about the tool rotational axis and to configured to move the tool with an advancing motion such that the active point of the blade shifts along the blade. The advancing motion is defined by a curve having at least a first radius of curvature and a second radius of curvature.

Claims

1. A device for machining a surface of a workpiece, comprising: a workpiece holder configured to rotate the workpiece about a workpiece rotational axis, a tool having a tool rotational axis and at least one blade having a blade radius of curvature, and a tool holder configured to position the tool such that an active point of the blade comes into engagement with the workpiece and to pivot the tool with a pivot motion about the tool rotational axis and to move the tool with an advancing motion such that the active point of the blade shifts along the blade, wherein the advancing motion is defined by a curve having at least a first radius of curvature and a second radius of curvature.

2. The device according to claim 1, wherein the tool holder is configured to perform the pivot motion and the advancing motion simultaneously.

3. The device according to claim 1, wherein the curve defining the advancing motion has a varying radius of curvature.

4. The device according to claim 1, wherein an angle of the pivot motion is determined based on the blade curvature and/or a curvature of the surface to be machined.

5. The device according to claim 1, wherein the tool holder is configured to move the tool along a first axis and a second axis, the first axis and the second axis being perpendicular to each other and defining a mounting plane of the tool, and wherein the tool holder is configured to rotate the tool around a third axis normal to the mounting plane of the tool.

6. The device according to claim 1, wherein the workpiece holder is further configured to move the workpiece along a fourth axis perpendicular to the workpiece rotation axis, wherein the fourth axis is inclined relative to the mounting plane of the tool at an angle of between 0? and 90?.

7. The device according to claim 1, wherein the surface to be machined is rotationally symmetric with regard to an axis of symmetry and has a curvature in an axial direction of the axis of symmetry.

8. The device according to claim 7, wherein the blade curvature is smaller than the curvature of the surface to be machined.

9. The device according to claim 1, wherein the tool holder is further configured to vary a speed of the pivot motion.

10. The device according to claim 1, wherein the at least one blade is made from a material having a hardness greater than a hardness of a material of the workpiece.

11. The device according to claim 1, wherein the at least one blade comprises two, three, four or five blades.

12. The device according to claim 1, wherein the at least one blade is inclined with respect to the surface to be machined at an angle of 100 to 30?.

13. A method for machining a surface of a workpiece, comprising: rotating the workpiece about a workpiece rotational axis, moving a tool having a tool rotational axis and at least one blade having a blade curvature such that an active point of the blade comes into engagement with the workpiece, and pivoting the tool with a pivot motion about the tool rotational axis and moving the tool with an advancing motion such that the active point of the blade shifts along the blade, wherein the advancing motion is defined by a curve having at least a first radius of curvature and a second radius of curvature.

14. The method according to claim 13, further comprising: parameterizing the surface to be machined, and determining the advancing motion based on the parameterized surface to be machined.

15. A bearing component, made by the device according to claim 1.

16. A system comprising: the device according to claim 1, and the workpiece.

17. A method for machining a surface of a workpiece, comprising: rotating the workpiece about a workpiece rotational axis, moving a tool having a tool rotational axis and a blade having a blade length and a blade radius of curvature such that an active portion of the blade comes into engagement with the workpiece, and moving the tool such that the active point of the blade shifts along the length the blade, wherein the moving occurs along a first curve having a first radius of curvature and along a second curve having a second radius of curvature, and wherein the active point of the blade has a length less than the blade length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a perspective view of a device for machining a surface of a workpiece according to an embodiment of the present disclosure.

[0027] FIG. 2 is a tool for the device of FIG. 1.

[0028] FIGS. 3A-3C illustrate the tool of FIG. 2 during a machining process.

[0029] FIG. 4 is a flow diagram of a method for machining a surface of a workpiece according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0030] In the following same or similar functioning elements are indicated with the same reference numerals.

[0031] FIG. 1 shows a device 1 for machining a surface of a workpiece 2. The device 1 comprises a workpiece holder 4 configured to rotate the workpiece 2 about a workpiece rotational axis A.sub.rw with a rotational speed n.sub.w. The workpiece 2 may be a bearing component such as an inner ring, an outer ring, and/or a rolling element.

[0032] The device 1 further includes a tool 6 having a tool rotational axis A.sub.rt. The tool 6 is arranged in a tool holder 8 that is configured to position and move the tool 6 with respect to the workpiece 2. In particular, the tool holder 8 holds and moves the tool in a mounting plane T.sub.m, wherein the tool rotational axis A.sub.rt is parallel to the mounting plane. The tool 6 can engage the external circumference of the workpiece 2 to produce a rotationally symmetric exterior surface of the workpiece 2. Also, an interior surface of the workpiece 2 can be produced. End faces of the workpiece 2 can also be machined if the tool rotational axis A.sub.rt is positioned perpendicular to the workpiece rotational axis A.sub.rw.

[0033] The tool 6 includes at least one blade 10 (FIG. 2) having a blade curvature defined by at least one radius. The tool holder 8 is further configured to position the tool 6 such that an active point of the blade 10 comes into engagement with the workpiece 2. In addition, the tool holder 8 is also configured to pivot the tool 6 with a pivot motion about the tool rotational axis A.sub.rt and to move the tool with an advancing motion such that the active point of the blade shifts along the blade 10. Preferably, an angle around which the tool is pivoted is determined based on the blade curvature. For example, the pivot motion and the advancing motion may be performed simultaneously. That is, the tool is pivoted while the tool is moved with advancing motion.

[0034] The tool holder 8 can also be configured to vary a speed of the pivot motion. The advancing motion is defined by a curve having at least a first radius of curvature and a second radius of curvature. Using an advancing motion having at least a first radius of curvature and a second radius of curvature allows to machine not only straight surfaces but also surfaces that are curved such as a raceway of a ball bearing.

[0035] In FIG. 1, the workpiece holder 4 is further configured to move the workpiece 2 along an axis A.sub.mw which is perpendicular to the workpiece rotation axis A.sub.rw. As can be seen from FIG. 1, the axis A.sub.rm and the mounting plane T.sub.m of the tool define an inclination angle ? between them, wherein the inclination angle ? is between 0? and 90?. Preferably, the inclination angle ? is 45?.

[0036] Furthermore, the tool holder 8 is equipped with a tool carrier 12 that can be rotated around the tool rotational axis. One or more circumferential tools can be arranged along the circumference of the tool carrier. If several tools are provided, they can be shaped identically so that when one tool 6 becomes worn out the tool carrier 12 can be advanced to a new tool. It is also possible to mount differently shaped tools on the tool carrier, which can then be used optionally to produce various surfaces. Even when several tools 6 are arranged on the circumference of the tool carrier 12, only one of these tools 6 is used at a time during the machining process.

[0037] The tool holder 8 is configured to move the tool along a first axis A.sub.1 and a second axis A.sub.2, wherein the first axis A.sub.1 and the second axis A.sub.2 are perpendicular to each other and define the mounting plane T.sub.m of the tool 6, as well as to rotate the tool around a normal vector A.sub.N of the mounting plane T.sub.m of the tool 6. A tool holder 8 configured as described above allows the tool to move in an advancing motion that has at least two radii of curvature and preferably a varying radius of curvature.

[0038] FIG. 2 shows the tool 6 of FIG. 1 in detail. The blade 10 is arranged at the tool 6. The blade 10 of FIG. 2 is shaped as a helical curve coaxial to the tool rotational axis A.sub.rt. However, the blade may have any other shape. For example, the blade may have an elliptical shape. Additionally or alternatively, the tool 6 may be provided with more than one blade, preferably two to five blades.

[0039] Furthermore, the blade 10 is made from a material having a hardness greater than a hardness of a material of the workpiece 2. For example, the blade may be made of cubic boron nitride (CBN), ceramic, and/or diamond. Furthermore, the blade may be inclined from 10? to 30? relative to the surface to be machined The blade 10 may be fixed to the tool with any suitable fastening method. In particular, the blade 10 may be press-fitted, interference-fitted, and/or materially bonded to the tool 6. For example, the blade 10 may be glued and/or fixed to the tool 6 with a tongue and groove connection.

[0040] FIG. 3A to 3C show how the tool 6 and blade 10 move over a surface to be machined 14. Because the blade 10 only engages with its active point 16 only relatively minor cutting forces occur, even in the case of a wider blade. As can be seen in FIG. 3A to 3C, the active point 16 of the blade 10 shifts along the blade 10 as the tool 6 is moved and pivoted.

[0041] FIG. 4 shows a flow diagram of a method for machining a surface of a workpiece. The method of FIG. 4 comprises the step S1 of rotating the workpiece 2 about a workpiece rotational axis A.sub.rw. Furthermore, the method includes the step S2 of moving a tool 6 having a tool rotational axis A.sub.rt and at least one blade 10 such that an active point 16 of the blade 10 comes into engagement with the workpiece 2, and the step S3 of pivoting the tool 6 with a pivot motion about the tool rotational axis A.sub.rt and moving the tool 6 with an advancing motion such that the active point 16 of the blade 10 shifts along the blade 10, wherein the advancing motion is defined by a curve having at least a first radius of curvature and a second radius of curvature. Preferably, the method further comprises parameterizing the surface to be machined, and determining the advancing motion based on the parameterized surface to be machined.

[0042] In summary the described method and device for machining a workpiece allows twist-free surfaces to be obtained without the need for additional machining processes such as grinding, belt grinding, superfinishing, machining in hardened material and/or finish rolling. The described method and device also allow for machining surfaces that are curved, particularly in a direction of the tool rotation axis. For example, the device 1 and method can be used to machine bearing components for various types of bearings such as tapered roller bearing, deep groove ball bearing, angle contact ball bearing, spherical roller bearing and/or plain bearings.

REFERENCE CHARACTERS

[0043] 1 device [0044] 2 workpiece [0045] 4 workpiece holder [0046] 6 tool [0047] 8 tool holder blade [0048] 12 tool carrier [0049] 14 surface to be machined [0050] 16 active point [0051] A.sub.mw axis along the workpiece is moved [0052] A.sub.rw workpiece rotation axis [0053] A.sub.rt tool rotation axis [0054] A.sub.1 first axis [0055] A.sub.2 second axis [0056] A.sub.N normal vector [0057] T.sub.m mounting plane [0058] S1, S2, S3 method steps